A. Field of Invention
This invention pertains to the art of methods and apparatuses for grinding various materials into smaller particles; particularly, to those known in the art as pulverizing systems and devices.
B. Description of the Related Art
Pulverizing systems with one or more disc mill assemblies are well known in the art. Pulverizing systems are used to grind pelletized or shredded plastics, nylons, polyesters and other polymers into powder; although it is to be understood that the invention could also be useful in other industrial applications. Such systems have traditionally included a hopper bin for storing input polymer materials, means for feeding the input material to the disc mill assembly, means for carrying the processed ground material from the disc mill assembly to a sorting module, means for transporting acceptable ground material to a ground material collection area, and a means for recirculating unacceptable ground material to a second disc mill assembly for further grinding (although single disc mill assemblies are also known, and intended to be covered by the claims of this application). Most disc mill assemblies typically include a spindle, a flywheel, both a rotating disc and a stationary disc with cutting surfaces (hereafter, collectively a “grinding disk” or “grinding disks”), a means for cooling the stationary grinding disk (e.g., a waterjacket), means for introducing air into the mill, and means for adjusting a distance between two facing cutting surfaces of the grinding disks. The grinding disks can be constructed of any material chosen according to sound engineering judgment; including those having a malleable substrate.
Broadly speaking, the pulverizing system operates by moving polymer materials stored in the hopper bin into the disc mill assembly, where the grinding disks—with cutting surfaces arranged in facing operative relation—progressively reduce the size of the input materials until they are of suitable size to exit the grinding channel by virtue of centrifugal force. The ground materials are then collected, and either stored, or re-circulated for additional grinding and/or processing.
Previously, disc mill assembly grinding disks were difficult to manufacture and maintain in operational condition. In order to accomplish the progressive grinding operation referenced above, grinding disks have traditionally utilized a tapered cutting surface. Specifically, prior art pulverizing systems utilized tapered grinding disks secured to planar flywheel and water jacket assemblies. The assembly and arrangement of two grinding disks with tapered cutting surfaces in facing relation creates a grinding channel with a gap of greater height nearer the center of the grinding disks than at their outer portions. Thus, input materials enter the disc mill assembly through material input openings in the inner portions of the water jacket and grinding disk, and are pulled outward by centrifugal force through a grinding channel with a gap of ever decreasing size—a process that progressively reduces the size of the input material until it is in a substantially powder form. Unfortunately, the manufacture of grinding disks having the aforementioned taper is difficult and expensive; it would be preferable to manufacture a grinding disk with a flat cutting surface having the same functionality of a tapered grinding disk. Thus, there is a need in the art for a grinding disk with a cutting surface that is flat when manufactured, but functionally tapered when assembled into the disc mill assembly.
Additionally, in order to withstand the forces exerted during the grinding operation, grinding disks have traditionally been heavy and thick metal devices. This permitted the grinding disks to be securely bolted or otherwise attached to the water jacket and flywheel, respectively, and allowed for their periodic re-sharpening (where the thickness of the grinding disk gradually is reduced until the plate became unusable). For example, the typical grinding disk becomes degraded in the normal grinding operation, and must be either replaced or re-sharpened, after only approximately 150 hours of use. Thus, grinding disks were traditionally returned to the manufacturer for re-sharpening after a relatively short period of use, and the costs associated with maintaining a pulverizing system included both re-sharpening charges and shipping fees for regularly transporting the heavy devices round trip for maintenance. As a result, there is a need in the art for a disc mill assembly that eliminates the high re-sharpening and shipping costs associated with the traditional grinding disk by cost-effectively permitting the user to replace rather than re-sharpen the grinding disks.
The present invention provides methods and apparatuses for an improved disc mill assembly that solves the aforementioned problems in the prior art.